Transport in Plants

Function of xylem and phloem

Xylem – brings water from the root to the leaves of the plants

Phloem – transports sugar from one part of the plant to another

Position of xylem and phloem

Water – taken up by root hairs From root hairs – towards the center Here it enters the xylem Xylem -> root -> stem -> leaf Transpiration - water evaporates from

plant cells and diffuses into air via leaf

transpiration In a leaf – water evaporates from wet

cell walls Air space inside leaf full of water vapor High concentration of water vapor

inside leaf than outside Water diffuses from inside to outside

through stomata into air This is traspiration

Transpiration stream

Uptake of water into root hairs

Root hairs grow down New root hairs grow behind the old

onesDie Lasts for less than a day Grow between soil particles Water enters via osmosis Increases surface area to speed up

osmosis

Root hair cross sectionHow water travels into the root:• passes through the cortex•No chloroplast in cortex cells •Moves towards the center of the root•Some goes into cytoplasm of cells, through the cells and into the next cell till it reaches the xylem•Most goes in between cells or though cell walls and never actually into cells.

Xylem vessels Made of long hollow dead cells placed

end to end to form a continuous tube Water enters through tiny holes in the

xylem called pits

Transpiration through leaf

Transpiration Water leaves xylem vessels and some

enters the mesophyll cells Water evaporates into air space as

water vapor (cuticle prevents too much water loss)

Water diffuses out of stomata into air Air takes away water vapor

Root hair cellsType of cells Function PictureRoot Hair cells:•Found on outside of plant roots/ above root tip• Long/ thin reaching out into soil

•Help anchor the plant to the soil•Absorb water mineral ions from soil•Has large surface area so that lots of dissolved nutrients can get inside the cell quickly

Xylem Cell:•Empty / dead cell• Cell wall fill with lignin – hardens / strong / waterproof / with cellulose• 1 cell = xylem vessel element – no end walls

• end to end formation – forming long continuous tubing from roots to leaves (1) transport water / minerals from root to parts of plant (2) structural support to plant (lignin)

Pathway of water Place in pathway

How water travels

Root hair By osmosis water enters root hairs. From here water passes into the root cortex

Root cortex Water moves more in between cells than through cells into the center towards the xylem

xylem In the xylem, water moves up the xylem due to the water potential gradient between the water and air. Water potential in air is less than water potential in roots and therefore the water moves up the stem

Mesophyll cells Water moves down the water potential gradient from the xylem vessel and into the cell walls of the mesophyll. This reduces the pressure at the top off the xylem vessel. The difference in pressure causes water to move up the xylem (root to the top)Water produces tension / cohesive (water molecules stick to each other)

Properties that allow water to flow upwards.

The cytoplasm of root cells usually have much higher total solute concentrations than water in the surrounding soil.

Thus, water diffuses into root cells by osmosis. Water must cross the cortex of the root to

enter the xylem. water moves by capillary action through cortex

cell walls until it reaches the endodermis. 90 % of water moves through the route this

way.